New cost function for motion estimation in MPEG encoding using LNS

The Logarithmic Number System (LNS) has lower power and larger dynamic range than fixed point, which makes LNS suitable for designing low-power, portable devices. Motion estimation is a key part of the MPEG encoding system. This paper introduces LNS into motion estimation for the MPEG encoding system. The block matching technique is the most commonly used motion-estimation method in MPEG encoding. The Mean Absolute Difference (MAD) is an inexpensive fixed-point cost function, which uses the sum of the absolute difference of the pixel values in the reference and encoded frames. Since LNS addition and subtraction are expensive, we propose the quotient of the two pixels' values instead of the difference. LNS division only needs a fixed-point subtractor. Similar to the absolute difference, we take the quotient of the larger value over the smaller value. We call this new cost function Mean Larger Ratio (MLR). The product of such ratios is calculated for each of the macroblocks in MPEG frames. Using MLR, LNS has approximately the same hardware as MAD for fixed point. Example videos show MLR provides a practical cost function to perform motion estimation with LNS.